The present invention is directed to a beam delivery system for use in pulsed laser deposition of a target evaporant onto a substrate. More specifically, it is directed to a scanning laser beam delivery system for obtaining optimally uniform deposition of a target evaporant onto the given substrate.
In known physical vapor deposition techniques such as sputtering, the coupling of energy and evaporant sources resulting from the free electrochemical interactions of the cathode, the target, and the sputtering gas makes uniform deposition extremely difficult. In contrast to these techniques, the pulsed laser deposition technique employed in the present invention essentially decouples in the deposition process the energy and evaporant sources such that uniform deposition becomes practicable. In a typical pulsed laser deposition arrangement, an evaporant source, or target, is placed within a vacuum environment along with, and in close proximity to, a substrate onto which the evaporant material is to be deposited. A pulsed laser beam generated by an energy source located outside the vacuum environment is directed into the vacuum environment to impinge upon a portion of the target. This causes the formation of a highly forward-directed evaporant plume which emanates from that portion of the target radiated by the pulsed laser beam toward the substrate. The particles contained in that evaporant plume are thereby deposited into the substrate's surface.
One significant drawback with the technique just described derives from the fact that the evaporant plume thus generated is characterized by a non-uniform distribution of its constituent particles. Much like the cloud of paint ejected from a spray paint can, the outer fringes of the plume tend to exhibit significantly less particle concentration than that exhibited in its central portions. Absent external means to compensate for or nullify this factor, therefore, uniform deposition, even with the pulsed laser deposition technique, remains very difficult.
One approach to addressing this inherent deficiency in the pulsed laser deposition technique, as envisioned by the present invention, is to introduce into a pulsed laser deposition arrangement automatically-controlled means for scanning that portion of the pulsed laser beam directly impinging upon the given target.
Obtaining high uniformity Of deposition, however, is not a trivial matter; and, measures must be taken in employing this laser beam scan to insure that the energy density of the laser beta radiation incident on the target is maintained at a constant level at all times during the deposition process. Moreover, measures must be taken to precisely control the laser beam scan so as to coordinate with any and all concurrent manipulations of both the target and substrate. Otherwise, deposition uniformity along all portions of a substrate deposition surface of more than a nominal surface area may not be realized.